Parts & Functions of a Computer Mouse

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Many mice have two buttons and a scroll wheel.
Image Credit: Ingram Publishing/Ingram Publishing/Getty Images

Mice are a basic peripheral component of all modern desktop computers. Mice send data to your computer that tells your computer where to display the cursor of your operating system's graphical user interface. While mice come in a variety of shapes and sizes, their basic parts and functions remain similar. Each mouse has at least one button for user input, a connection to the computer and a way to track motion.



The button or buttons of a mouse constitute part or all of the top surface of the mouse. When you press a button, it tells your computer to perform an action at the cursor's location on the screen. A mouse has at least one button, though most have two or more. On some mice, such as the standard mouse for many Apple desktop computers, the entire top surface of the mouse is a single button. Two-button mice allow you to input different messages to your computer depending on whether you click the right button or the left button. Your computer interprets these different clicks based on the configuration of your mouse driver.


Motion Detection

Your computer needs to receive data about the motion and location of your mouse. The two most common components for picking up this data are the trackball and the optical sensor. The trackball is a small ball inside a cavity underneath the mouse. As the trackball rolls across a surface, internal gears encode data about the mouse's position. Trackballs require some maintenance, as the cavity can fill up with dirt and debris, thereby causing inaccuracies in the motion data. Optical mice use an optical sensor to track the mouse's movement across a surface. This is less susceptible to errors caused by the intake of dirt and debris, but the optical sensor may perform differently depending on the reflective properties of the mouse surface. A third and less common motion sensor is the internal gyroscope. These eliminate the need for any sort of contact between the mouse and a surface.


Scroll Wheel

Many mice have at least one wheel used to send scrolling data to the computer. Standard mouse drivers interpret scrolling data according to the current window in your GUI. For example, if your current window is a browser window, the scroll wheel will enable you to scroll up and down that window. On many mice, the scroll wheel also functions as a third button. In some cases, pressing the scroll button will toggle a scroll mode on or off. This mode allows you to scroll by moving the entire mouse instead of by rolling the wheel.



Your mouse can't transmit data if it isn't connected to your computer. Some mice connect to your computer via a cord, while others are cordless. If your mouse has a cord, it is likely a USB cord that fits into your computer's USB port. Earlier mice utilized different connections, such as serial or PS/2 ports. Cordless mice connect to your computer by transmitting infrared or radio signals. Radio signals sent by your mouse are also known as Bluetooth signals. Both infrared and Bluetooth signals require a detector on your computer. Typically, you connect this detector to a port on your computer. The detector will receive your mouse motion data and transmit it to your computer. In order to send these signals, your mouse must be powered by batteries.